Analog signal waveforms recorded by physiolosical signal recorders such as electrocardiographs are required to be accompanied by certain data such as the names of patients, the dates of recording, the speeds at which the recording sheet is fed, the degrees of sensitivity, or analitic results of somatic signals.
U.S. Pat. No. 3,754,279 discloses a recorder including a theremal print head for recording identifying numerals on a recording sheet at predetermined intervals. A recorder is also well known in which a separate theremal print head is supplied with character and symbol data from a character generator. Since these recorders utilize thermal print heads, however, they are not suitable for use with recording pen using ink. Furthermore, with the separate thermal print head, a space on the recording sheet where signals are to be recorded is large, with the result that the recorders are expensive in manufacture.
A solution to the above shortcomings would be to make the recording pen to record characters by converting digital signals from the character generator into analog signals which are then supplied to the recording pen. Since the recording pen used in the electrocardiograph and the like is always in contact with the recording sheet for continuously recording signals having a frequency up to about 100 Hz, however, it is almost impossible to record characters in dots in response to intermittent signals coming from the character generator. More specifically, each time the date read out of the character generator change from "1" to "0" or from "0" to "1", the recording pen is returned to a base line, in which case, as shown in FIGS. 2b and 3a, unnecesary vertical lines are recorded in addition to dots that constitute characters, thereby making the characters look indefinite. With such an arrangement, it is extremely difficult to distinguish between characters that look similar such as "F" and "P" , or "C" and " O". Additionally, no consideration has been given to the relation between the length and width of characters recorded, resulting in a difficulty in recognizing what the recorded characters are.